With advances in medicine and conceptual increments of modern medical care, more and more attentions have been paid to fast, inexpensive, small-volume, and self-test product which does not require for professionals to operate (such as blood glucose meters, electronic ear thermometers, and electronic sphygmomanometers, etc.). In both medical and biochemical assays, using an electrochemical test strip has already been a common technique. Conventional electrochemical test strips includes at least two measuring electrodes. After the sample is injected into the reaction region of the test strip, characteristics of the sample can be measured by at least two measuring electrodes. Under such construction, however, whether the sample has been completely covered the measuring electrode is unable to be determined prior to operating measurements. Moreover, whether the sample is injected and entered into the reaction zone is unable to be ensured.
With reference to currently background art, there are a variety of technical solutions existed to solve the background problems. For example, U.S. Pat. No. 5,582,697, the entity of which is incorporated herein by reference, discloses an electrochemical test strip with three electrodes. A third electrode is introduced in the reaction region and placed the most distant from the entrance of the reaction zone compared to the other two measuring electrodes. After injection of the sample, by detecting the current change of the two measuring electrodes between the closest to the inlet and the farthest from the entrance in the reaction region to determine whether the sample properly covers these measuring electrodes. Another U.S. Pat. No. 6,743,635 discloses an electrochemical test strip with four electrodes. In addition to the first and second electrodes, a third and a fourth electrodes are introduced in the reaction region and placed the most distant from the entrance of the reaction zone compared to the other two measuring electrodes. After the sample is injected into the reaction region by capillarity, the third and fourth electrodes are electrically connected by using the capacity of conductivity of liquid samples, thereby confirming that the sample covers the measuring electrodes. The methods to determine the status of sample discloses in U.S. Pat. Nos. 5,582,697 and 6,743,635, however, cannot accurately detect whether the sample fully covers measuring electrodes. For example, referring FIGS. 4A-4E, when an insufficient amount of sample enters into a reaction region of an electrochemical test strip, the sample partially covers the ends of the measuring electrodes due to a hydrophilic structure of electrochemical test strip and capillary action. The third electrode of U.S. Pat. No. 5,582,697 and the third and fourth electrodes of U.S. Pat. No. 6,743,635 still can be electrically conducted, enforcing the detection equipment to perform concentration detection. However, the sample volume is insufficient, resulting in incomplete chemical reactions on the measuring electrodes, severely under-estimated measurement data, and erroneous measurement results.
As to other related background art, Taiwanese Patent No. 1388823 discloses a third electrode added in the reaction region. The third electrode is placed the most distant from the entrance of the reaction zone compared to the other two measuring electrodes. With this third electrode in operated with measuring electrodes, capacitance value of the sample can be measured, and the sample volume can also be determined. In addition, U.S. Pat. No. 7,452,457 discloses an electrochemical test strip with at least three electrodes. A third electrode is placed the most distant from the entrance of the reaction zone compared to the other two measuring electrodes. With the use of AC signal to measure the reaction amplitude or phase angle of the test sample, the sample volume can therefore be calculated. During the process for detecting the electrochemical concentration, the sample contains many substances with electrical reaction signals. For example, during the process of blood measurement, hematocrit volume will seriously affect the measured capacitance value. The concentrations of glucose and uric acid affecting on the magnitudes of reaction signals will cause inaccurate determination for measurement systems disclosed in Taiwanese Patent No. 1388823 and U.S. Pat. No. 7,452,457. This is attributed to only considering by reference with a single reaction signal, resulting in ineffective determination of insufficient sample volume as shown in FIGS. 4A-4E and failure judgement of the measuring system.
Further, each of the abovementioned background art requires at least one dedicated electrode additionally set in a place the most distant from the entrance of the reaction region to proceed with measurement for the sample volume, resulting in volume increment of test strip and sampling. Accordingly, an electrochemical test strip configured to correctly identify the sample volume and with reduced number of electrodes is needed for the industry.